Method for bulk sorting shredded scrap metal

Abstract

A stream of shredded scrap metal is divided into increments. A bulk material analyzer is employed to determine the bulk chemical composition of each increment. The increments are then sorted on the basis of the bulk chemical composition of each increment.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims the benefit of U.S. Provisional Application No. 61 / 037,838, filed Mar. 19, 2008, and the disclosure thereof is incorporated herein by reference.FIELD OF THE INVENTION[0002]The present invention relates generally to the processing of scrap metal and more particularly to the processing of shredded scrap metal.BACKGROUND OF THE INVENTION[0003]Shredded scrap metal is produced typically by feeding obsolete or discarded articles of metal (i.e., scrap metal) into an apparatus called a shredder in which the scrap metal is flailed, by rotating, free-swinging hammers, into relatively small, fist-sized pieces that, after further processing, provide a densified scrap charge in a melting furnace. A typical feed into a shredder comprises whole junk autos, discarded appliances, scrap metal recovered from demolition projects, light gauge other obsolete steel scrap and some heavier obsolete steel scrap.[0004]The output product of th...

AI Technical Summary

Benefits of technology

[0035]The method may be employed to further reduce the copper content of shredded ferrous scrap from which attached and commingled copper (including “meatballs”) has been previously removed by manual pickers or by some other procedure for removing such copper. In such a case, the copper content of the shredded ferrous scrap (e.g., 0.14% Cu) is due at least primarily to metallurgically incorporated copper, i.e., copper that is present in the steel internally, either as an impurity or as an intentionally added alloying ingredient. Those increments having a copper content greater than a predetermined amount (e.g., greater than 0.20% Cu) are diverted from the stream. The undiverted increments are accumulated downstream of the bulk sorter; the accumulation of undiverted increments has an average copper content less than that obtained merely by removing attached and commingled copper and is thus more useful as a feedstock for producing flat rolled steel.

[0040]In another embodiment, the method may be employed to divert, from a stream of shredded ferrous scrap, increments having one or more desirable alloying ingredients employed in alloy steels (e.g., chromium, nickel, molybdenum); and these increments are accumulated in a stockpile to be sold as a separate material for use as a feedstock for producing alloy steels. A related embodiment produces a stockpile having a composition that contains not only one or more of Cr, Ni and Mo but also contains copper, thereby enabling the stockpile to be used as a feedstock for producing alloy steels that are resistant to atmospheric corrosion. All of these feedstocks are materials of increased value.

Problems solved by technology

Shredded ferrous scrap unavoidably contains pieces of tramp, non-ferrous scrap that are physically attached to or entangled with pieces of ferrous scrap by fasteners or the like, or otherwise attached, and as a result, have been carried over with the ferrous scrap pieces to which they were attached, during magnetic separation.

Copper is undesirable as a constituent in a steel melting furnace charge for making a product known as flat rolled steel which is flawed by the presence of copper in excess of a specified maximum amount above which the steel is rendered unfit for its intended uses (e.g., deep drawing).

Copper cannot be removed from a bath of melted steel by refining.

There are some steel products that are unaffected by the presence of copper in amounts that adversely affect flat rolled steel.

88-92), and shredders have been in widespread use for the processing of ferrous scrap for several decades; but the problem of excess copper content in shredded ferrous scrap has still not been solved to the entire satisfaction of consumers of that scrap.

Non-ferrous sorting systems that analyze or detect individual, spaced apart fragments of shredded scrap and sort them with air jets or mechanical fingers, on a piece-by-piece basis, need to screen for size the particles of shredded scrap and maintain a particle size within maximum and minimum limits, or the sorting accuracy suffers (Id., p.

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